134 MODERN METHODS OF TESTING MILK 



milk falling below the fixed limit in composition is 

 regarded as adulterated. Thus, a standard common 

 to several states is 12 per cent, of solids and 3 per cent, 

 of fat. This means also that such legal-standard milk 

 must not contain more than 88 per cent, of water or 

 less than 9 per cent, of solids-not-fat. 



The relations of the different constituents of milk 

 have been studied and formulas have been devised 

 which enable one in an approximate way to tell how 

 much water has been added to a sample of milk be- 

 yond the amount allowed by the standards. These 

 formulas are based on the assumption that the limits 

 fixed by the legal standard represent the lowest 

 amounts of solids and fat found in normal milk, and 

 they are correct only when the original milk contains 

 the lowest percentages given in the legal standard. 



In calculating the amount of added water in milk, 

 the amount of solids-not-fat (total solids minus fat) 

 is used as a basis. The procedure is as follows : 



(i) Determine the per cent, of fat in the suspected 

 sample. 



(2) Take the lactometer (Quevenne) test. 



(3) Determine the amount of solids-not-fat ac- 

 cording to the formula, ^L+.2f. (p. 129). 



(4) Apply the following rule: Multiply the per cent, 

 of solids-not-fat by 100 and divide the result by the 

 legal standard for solids-not-fat. Subtract the last 

 result from 100 and the result is the per cent, of ad- 

 ded water in the sample of suspected milk. This rule 

 is expressed in the form of the following formula : 



T. 4. f jj J i per cent, of . solids-not-fat X 100. 



Per cent, of added water=ioo—, ,- , ,. ,., -. . 



legal standard for sohds-not-fat. 



